Carbosilanes Cross-linking

The carbosilane is a white, soluble, and meltable material that can be melt-spun into fibers at 190 °C. Exposure of the fibers to air at the same temperature generates a surface coating of silica which stabilizes the structure throughout the cross-linking step prior to pyrolysis. Subsequent heating at 1,200-1,500 °C in a nitrogen atmosphere drives off... 

A considerable amount of subsequent research and process development has been carried out to produce silicon carbide with a reduced level of excess carbon via processes that allow more facile cross-linking.2 -32 Several hundred papers and patents on this topic exist in the literature, and only a few examples will be mentioned here. One process development involves the slurry spinning of fibers in place of melt spinning.33 In this process, silicon carbide powder, made by a conventional industrial process, is dispersed in a solution of carbosilanes in toluene. The syrupy paste is spun into fibers and then pyrolyzed to silicon carbide. These fibers are reported to be stable at 1,500 °C for 120 hours. 

We have described a new system of polymeric snpports based on multifunctional, exceptionally sterically hindered carbosilane moieties, grafted with block poly(vinylmethyl-co-dimethyl)siloxane arms. They offer uniformly periphery-distribnted active sites (-CH = CH moieties) and can be used for preparation of novel catalysts. Platinum was thus attached to the polymers via coordination to vinyl gronps. The materials used in hydrosilylation of vinylsilanes can be considered as an alternative for traditional platinum catalysts. The utility of the catalysts seems to be dependent on the ratio [D]/[V] in the copolysiloxane arm. Those with too high amonnt of vinyl groups suffer from poor solubility and catalytic performance dne to excessive inter/intra-chain coordinative cross-linking. 

In these copolymerizations, the polymers with the vinylmethylsilane group are of interest, because the presence of the vinyl group would assist cross-linking if the polymers are used as precursors for SiC. Both IR and NMR data indicated that the vinyl content in the polymer is lower than expected and that some carbosilane may form. The yields of SiC were good (Table I). 

The thermal treatment of vinylic polysilane SiC precursor polymers involves <300 °C cross-linking and loss of low molecular weight oligomers. Polymer degradation, which is characterized by significant decomposition of the side groups and chain scission, along with conversion of the polysilane skeleton to poly(carbosilane), takes place between 300 and 750 °C [124],... 

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